1. Field of the Invention
The present invention relates to a halftone images, and more specifically, to a method of adjusting the position of dots in the halftone image for improving image quality.
2. Description of the Prior Art
Halftoning describes the process of displaying an image on a device which is capable of representing only a finite, discrete number of tone levels. The position and arrangement of the discrete picture elements should create the illusion of a continuous-tone image. Using traditional halftoning techniques such as error diffusion or dithering matrix, undesirable visual patterns often appear, caused by the fact that the dots are placed along a distinct, rectangular (or sometimes hexagonal) grid.
Please refer to FIG. 1. FIG. 1 is an original halftone image 10 according to the prior art. The halftone image 10 is created according to techniques well known in the art, such as through error diffusion or dithering matrix algorithms. The halftone image 10 contains a plurality of pixels, each of which contains either a dot to be printed or a blank space. For instance, in FIG. 1, pixel 12 contains a blank space whereas pixel 14 contains a dot to be printed. Unfortunately, the dots in the halftone image 10 sometimes appear too close together, and form large block patterns in the images printed from the halftone image 10. For example, near the top-left corner of the halftone image 10 is a block 16 of three pixels containing dots to be printed. Because the three pixels in the block 16 are all contiguous, the block 16 looks like one very long pixel instead of three separate pixels. The end result is that the halftone image 10 contains many undesirable block patterns, and the quality of printed images suffers.